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Integrated Robot Controller.
Designing and building a robot control system was not an easy task
as it was first thought. After making a series of four controllers
I think I have come to a point where I am very happy with this
finished design. All the previous three designs worked extremely
well, but this design is a much more compact design of the four.
The first one built used discrete units and achieved steering,
speed control, failsafe and weapons firing. The second and third
controllers used a Parallax STAMP, however this new controller
uses two Arizona Microchip PIC controllers to perform the total
function of controlling the motion of the robot. The controller
detailed here is the fourth in a series designed for our robot, PC
Plod.
All
the
controllers
built
were
essentially
designed
to
perform the same task. The size of the electronics package has
shrunk significantly from the original design to the package you
see described here.
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K.R.Ginn
The history of the control system goes back a number of years
where in the original, which was very hurriedly put together.
Steering was achieved with a number of R/C switchers operating
four relays. Two of those relays were used for motor enabling
(steering),
whilst
the
last
two
were
used
for
motor
current
reversing. The failsafe was a commercially available unit, and the
speed controller was a hybrid. The very first speed controller was
made from a Futaba model speed controller, and a pair of motor
drive amplifiers. The amplifiers taking the current handling well
above the motor stall current (a minimum of 40 amps per motor).
Also the drive voltage and current the Futaba speed controller
could possibly cope with was not high enough for the drive motors.
The relays used to effect motor current switching were a little
under-rated (25 amps), but did not appear to suffer any undue
problems by virtue of their rating, i.e. running up to 40 amps
during a stall condition.
The two 24 volt permanent magnet motors used in the robot were
sourced at a grand price, second hand and complete with gearboxes
at £10 each from a local wheelchair supplier/repair shop. These
were found to be approximately 150 watt motors and delivers enough
torque to drive the robot. The calculated stall current of these
motors was found to be in the order of 40 amps each. The previous
and
this
current
design
should
be
more
than
capable
at
withstanding the stall currents of the two drive motors. A trip or
overload circuit is set to function and close down the drive at
about 47 to 50 amps. That is approximately 20 - 25% above each
motor stall current.
Radio Control systems
The R/C receiver signal (servo) format adopted in this unit has
followed what must be a very common format amongst radio control
systems.
That
being
a
variable
pulse
width
that
varies
under
command from the transmitter joystick between 1.0 and 2.0mS. This
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K.R.Ginn
pulse is updated every 20mS. The pulse is a positive edged pulse
of an amplitude of no greater than 5.0v. This can be used on most
40MHz land based radio carrier based R/C systems.
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K.R.Ginn
An outline of the principle parts.
The basic controller consists of five discrete parts, they are all
outlined below. The whole robot controller can run with only three
of the six circuits (PCBs), if desired. Omitting the failsafe PCB
and the two overload circuits. All the circuits were included to
show
the
total system
working
and
can all be
incorporated
if
required.
The H-Bridge – Motor Driver.
The H-bridge design uses a series of FETs to switch the motor
driver
current
flow;
–
four
drive
FETs
arranged
in
an
"H"
configuration. But as it is shown here, in this illustration (fig
1), as a series of four switches all actuated by a controller. The
controller is not shown in the diagram for clarity. The drive
motor is connected as shown between the two pairs of switches
(FETs), being the horizontal bar of the "H". Consider closing
switches S1 and S3, you will note that the current will flow
through S1 through the motor, left to right, and through S3 before
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K.R.Ginn
completing
the
current
path
back
to
the
power
source.
Alternatively only S2 and S4 switches could be closed, the other
two
being
open circuit,
now
you
will see
the
current flowing
through the motor, in this latter configuration from right to
left. The motor will rotate in the opposite direction. Having now
a means to control current through the motor, and motor direction,
albeit very crude, we can achieve forward, reverse motion of the
motor (robot/model) and stop function to by having all switches
open. The condition where S1 and S2, or/and S3 and S4 are closed
should be avoided at all costs, as this will short out the power
source and provide no means of driving the motor. The only result
here would be to have these devices destroy themselves, having
taken a short circuit current from a high power source. Since the
limiting current from a pair of series connected 12 volt lead acid
gel cells will be far greater than 200 amps, and may destroy
themselves having been shorted out!
As illustrated in figure 1 this controller has only basic control,
i.e. forward/reverse and stop. What is needed is some form of
variable drive to be applied to the switches. Using as mentioned
before the use of FETs is employed to control the motor drive
current. Using one switch to enable current flow, for example S1,
and to rapidly switch on and off S3, varying the mark-space ratio
will effect the forward rotation speed of the motor, but also the
speed can be selected between two limits. Using the other pair of
switches (FETs) to control the reverse current flow gives control
over the reverse rotation of the motor. Switching all switches
(FETs) off enables the motor to stop, no drive current.
Steering.
There are basically two types of steering, the first one being
differential steering, where power is applied to the two drive
motors, the rotation of one motor is less than the opposite side,
and
the
robot
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will
turn
towards
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the
slower
side.
Or,
tank
K.R.Ginn
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K.R.Ginn
steering, where both motors are driven at the same speed, and to
effect steering of the robot, one motor is driven in reverse to
the
other.
routine.
Thereby
demonstrating
that
"turning
However the differential steering robots
on
the
will
spot"
exhibit
essentially the same routine if driven so. The tank steered robot
is generally harder to drive. Because of the constraints in a
combat arena, it was thought better to have tank steering due to
the
tight
spaces,
and
better
manoeuvrability
the
tank
steered
robot has. However, tank steering has one major disadvantage; it
is
harder
to
control
the
robot
using
this
method,
whereas
differential steering has a more natural feel and steers much more
like a conventional motor vehicle or R/C model car. This type of
steering
was
used
on
the
previous
controllers,
and
has
been
dropped for tank steering in this design.
Failsafe
The failsafe is by far the most important part of the unit's
electronics package and is integrated within the routine of the
circuit and the programmed micro controllers. Here there are two
power supply circuits from the main motive batteries, one low
current and one high current path. The low current path, capable
of supplying no more than an amp or so, this supplies only the
controllers electronics, and the high current path which supplies
power to the drive motors, weapons and any ancillary circuitry.
The reason for providing the two distinct circuits is simply to
supply continuous power to the units electronics whilst the robot
is running, albeit if the robot is working and running around, or
sitting idle. The other condition is where, during failsafe, the
robot's power to drive motors and weapons will be removed for the
duration of the failsafe or overload condition. This will occur
under command of the micro-controller circuitry.
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Both
the
master
low and high current circuits are controlled
link.
When
removed
will
render
the
robot
in
by one
a
safe
condition, and no power will be supplied to any electronics in the
robot. You could call this a "Master Switch", and is essential for
any robot.
The failsafe condition occurs when the received signal from the
R/C receiver falls outside specific parameters. This happens when
the micro-controller circuits measure the incoming R/C receiver
pulses with a width duration less than 0.9mS, or greater than
2.1mS. This can occur during a time where there is an interfering
signal on the same or close to the R/C radio frequency, or if the
received signal is lost totally from the transmitter.
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K.R.Ginn
Power is removed from the high current circuits during failsafe
with the aid of a relay or series of relays governing power to the
motors,
weapons
condition
is
and
over,
any
the
ancillary
high
circuits.
current
path
Once
the
failsafe
supplying
power
to
weapons and motors is enabled and the robot can function after a
four second delay.
Over Current protection
This circuit is optional and can be installed and used to offer
additional protection to the drive motors and the controller's
drive circuitry under overload and extreme stall conditions. This
example is set to limit the total drive current to the controller
to maximum of 50amps to each motor (adjustable to between 40 to 50
amps - Rv1 on the board). Full clockwise rotation of Rv1 gives a
trip
current
of
40amps,
fully
anti-clockwise
gives
a
50
amp
setting). Even though the FET’s (intelligent switches; TR6 and
TR8)
are
themselves
are
thermally
protected
and
over
current
protected to 100 amps. The motor overload current (the trigger
point set by Rv1 on the overload circuit) has to prevail for
approximately three seconds before the overload circuit will trip,
it
will
then hold off the power and drive to the motors for
approximately five seconds and then re-apply power to the high
power circuits. If a short circuit, for example still prevails,
the circuit will cycle around the fault. The only way to stop the
circuit
cycling
would
be
to
deliberately
set
the
unit
into
failsafe by turning off the R/C transmitter or removing the master
link.
This Control System
This unit is designed to operate at 24v and control a pair of DC
permanent magnet motors to a maximum power of approximately 150
watts. I see no reason why higher power motors can’t be used with
this circuit. This would mean the controller would be able to
drive a pair of 24 volt motors drawing current in the region of 20
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K.R.Ginn
amps for each motor. Of course the amount of current drawn will
depend upon the load of the motor. Each motor drive circuit is
capable of delivering some 40 amps (stall current) per motor with
ease.
There
is a current limit set with
this controller
with
additional circuitry that will switch the main motor drive off for
five seconds during what could be an extreme motor overload, or
motor fail condition. This would be an additional safety feature
which would limit the current during a condition a little more
serious than a stall. Thus switching the motor drive off, since
the stall or fault current of such motors could well develop as
waste heat in the controller, motor and wiring in the region of a
kilo-watt or more.
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This unit will perform the functions of forward and reverse speed
control,
steering
(tank
steering),
failsafe
and
operation
protection circuitry. Weapons switching/firing can be accomplished
with the aid of an external unit, such as an R/C switcher. Since
the weapons used could be activated either as a simple on or off
function, or a sequence of functions needing more than a single
relay or switch function to operate. Additional switchers can be
used for additional functions within the robot, or indeed this
controller could be used for a large scale R/C model and is not
confined to the exclusive use of a combat robot.
The circuit
The control system here is built from two major parts, first one
being the micro controller circuit, the second part being the
motor drivers.
There are two motor drivers, one facilitating
drive for each motor, one the left hand side, the other driving
the wheel and motor on the right hand side of the robot. One micro
controller circuit supplies control for both motor drivers.
There
are
additional
circuits
which
are
optional
to
the
main
controller and can be added if the builder so desires. They are,
the failsafe relay driver and the protection circuits for the
motor drives. These are separate and can be located away from the
main circuitry, but in the prototype here, they are accommodated
close to the main electronics package of the robot.
Power for the electronics package is all derived from the onboard
main
motive
batteries
-
twenty
four
volts
(2
x
12v
15AH
gel
cells), including the power for the R/C receiver. The sensitive
electronics and the R/C receiver are all powered from an isolated
DC supply of five volts. The drive circuitry for the drive motors
is derived directly from the main supply. The choice of a 1 watt
DC/DC converter or in the prototype, a 3 watt DC/DC converter is
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K.R.Ginn
used to step down the 24 volts supply to 12v, and also to isolate
the main voltage source to the R/C receiver. The output from the
DC/DC converter is fed to a bank of three 4,700uF capacitors in
parallel, totalling some 15,000uF. Then on to a low voltage drop
out 5v three terminal regulator. The 12v feeding the regulator has
enough capacity to withstand, in operation, a considerable drop in
supply voltage of no less than three seconds to the main circuit
shown here. This stops the two PICs from resetting, and helps the
micro controller circuit when the unit is under very high load
conditions. These very high loads cause drops in supply voltage,
albeit momentarily from the gel cells. This is due to the internal
resistance of the batteries and wiring’s resistance losses causing
a transient voltage drop to as little as 15 volts for a period of
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K.R.Ginn
100mS or so. Enough time to possibly cause the whole circuit to
re-initialise.
The main twenty four volts supplied from the motive batteries,
will vary considerably with load and voltage transients. Under a
stall or starting load conditions the voltage could well drop to
fifteen volts from it's nominal value of twenty four. Conversely
it could rise to well above eighty volts with transients, i.e.
back emfs generated by motors and cabling itself. Therefore power
derived for the electronics package has to take into account all
these
possibilities. Because of the
voltage
variants,
specific
precautions have been designed into the circuit which account for
these possibilities.
Take
into
account
the
supply
voltage
to
the
micro
controller
circuit. The main twenty four volt supply is fed to this circuit
via
SK1.
Following
the
input
to
the
circuit
there
is
power
transistor TR1, a TIP41C power transistor. TR1 is biased into
conduction by R1 so that there is little voltage drop across the
collector emitter junction of TR1. Should the supply voltage on
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K.R.Ginn
the power line rise to a value to cause the zener diode D2 onto
conduction, this will have the effect of limiting the input supply
voltage to the DC/DC converter that follows TR1, that being 26
volts. This part of the circuit is designed only to reduce any
voltage transients that may appear on the main power line to the
DC/DC converter. It is not designed as a high power pre-regulator
to be fed constantly from a higher voltage source. Nominally the
input voltage should be twenty four volts, and will rise to about
twenty seven volts when the batteries are fully charged. D1 is
providing reverse polarity protection. An additional Varistor is
attached to the input side, external to the board, to help adsorb
any transients above 40v.
This Varistor (shown as R1 on the
overall circuit diagram) is attached to the 4-way plug feeding
power
to
the micro
controller
circuit and is
external
to the
actual micro board.
The 3 watt DC/DC converter provides a dual function, not only does
it serve to isolate the main supply, but it provides an efficient
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voltage conversion from 24 to 12v DC. Following the output of the
converter is a diode D3 which stops any of the charge from the
following
three capacitors
from discharging
through the
output
circuitry of IC1. The three 4700uF capacitors, enough hold charge
for at least three seconds for the low drop out five volt three
terminal regulator (IC2) which is used to feed a stable voltage
(5v) to the two micro controllers, IC3 and IC4. It also supplies
power to the R/C receiver.
The R/C receiver is fed with this regulated 5v supply, an option
is available where removing the link LK-1 will enable the R/C
receiver to be supplied with power from separate source, i.e. a
set of Nicads attached to the R/C receiver. The on-board 5v supply
on the micro controller board is actually adequate to drive the
R/C receiver.
The R/C receiver supplies a standard form of signals to the servo
outputs, the familiar 1.0 to 2.0mS pulse repeated every 20mS. This
is fed to the two PIC micro controllers, IC3 and IC4 through
PL2/SK2 and PL3/SK3. The two micro controllers then process the
R/C
signals
to
perform
the
functions
of
speed,
failsafe
and
steering. R4 and R5 bias the PIC inputs to zero volts.
Why the two PICs?
Considering
a
fairly
standard
R/C
model
installation,
and
illustrated in this following example we could have four servos
attached and controlling four functions of a model aircraft. Three
operating
the
controlling
control
the
engine
surfaces
on
the
speed.
Each
of
model
the
and
four
the
fourth
servos
works
independently of the other three in the model. Although there
could be mechanical interaction between the model’s servos, there
is no electronic interaction. If one PIC were employed in this
robot
controller
circuit
there
would
be
a
timing
problem
encountered. As we are integrating two primary functions within
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K.R.Ginn
the one control system; this being steering and speed control.
Examining the timing of the pulses from the R/C receiver in one
specific
case,
for
example;
channels
1
and
2
were
used
for
steering and speed/direction (forward and reverse), and channel 3
used to fire the weapon. Looking at the timing of the servo pulses
from the R/C receiver we have to consider the falling edge of the
first channel pulse, this was found to be only micro seconds in
front of the rising edge of the second pulse. Using one PIC to
control the robot would not have been sufficient. As the PIC could
not respond that fast to a break of micro seconds and perform the
routine programmed into a single PIC. This would mean the data
from the R/C receiver would be skipping each alternative receiver
servo pulse it received. Alternating between speed and steering
signals, this was considered undesirable. Two R/C receiver output
pulses have to be measured to enable the controller to perform
correctly. Each output is measured, and the two PICs work out in
what direction the robot is moving, if any.
It was therefore decided to dedicate a single PIC to each R/C
receiver output. Besides using one PIC to perform it's dedicated
function, either speed control or steering, the PIC would have in
it's own routine a portion of a failsafe routine written within.
This would be to disable the main drive motors and remove power to
any
high
current
circuit
during
a
failsafe
condition.
In
an
overload condition the power would be removed totally from the
drive motors and weapon.
The PICs
The
PICs
are constantly
looking at
the
two R/C servo outputs
feeding PWM signals to the controller. The PICs perform their
specific function, IC4 the speed control and IC3, the steering.
IC4 is constantly looking at the signal assigned for speed. IC3 is
constantly looking at the channel assigned for steering and feeds
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K.R.Ginn
information to IC4 which controls the functions for the steering
of the robot.
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The steering function, i.e. motor switching for both motors is
accomplished with a mixture of both signals and whereby a map is
produced internally to IC4. There are six active regions and three
in-active
regions
of
the
controller
under
normal
operating
conditions.
Both PICs look for valid signals in the window of 0.9 to 2.1mS.
IC4 closes down motor drive during failsafe, and IC3 is effective
during failsafe and overload. During failsafe the failsafe relay
is de-energised, and during overload from the sensor, will perform
the
same
function
as
is
found
during
failsafe
and
again
de-
energise the failsafe relay.
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IC4 is designed to control forward and reverse speed in one of
four forward or one of four reverse speeds. This will go from
approximately 10% to a full 100% speed.
Programming the PICs.
The PICs here are sourced through EPE, for those constructors who
have a PIC programmer these can be programmed by yourself. IC4 is
configured during the process of programming with the “power up
timer” – enabled. The oscillator setting set to “XTAL” as the
master oscillator. The clock for IC3 is slaved off the crystal
oscillator in IC4, and as a consequence, the “power up timer” is
enabled in the second PIC, and the oscillator setting is set to
HS, as though it was being fed from a high stability oscillator
module.
The code for both of the PICs in the controller was written using
Crownhill Associate’s Proton Plus PIC compiler- Version 2.1.5.3.
This made the task of writing and refining the PIC code very easy.
Converting
the
code
to
alter
the
steering
function,
to
differential steering - if required, should also prove to be an
easy task.
The rest of the circuit
Bearing in mind the sensitive electronics which includes the two
PICs and the R/C receiver, they are all isolated from the main
power supply, the outputs to the high power circuits are still
isolated with the use of a series of opto-isolators. Including the
failsafe function.
An exclusive OR gate (IC6a and IC6b) is used on each motor driver
in the controller as an added precaution to stop both this fault
condition
File: IRC01.doc
where
one
pair
of
FETS
Page 20 of 41
can
both
be
enabled
and
K.R.Ginn
effectively short out the supply. Should this happen for whatever
reason, the motor drive enable line is pulled high by R12 in the
motor driver boards, thus stopping all drive to the motor drive
FETs.
LEDs D4 and D5 on the controller circuit function as a signal path
to indicate a turn. With D5 illuminated, this indicates a left
hand
turn,
and
D4
illuminated
a
right
hand
turn.
The
LEDs
extinguished indicates either the controller is set to a straight
run
forwards
or
backwards,
or
in
neutral
and
in
the
stop
condition. Or indeed the unit could be in a failsafe mode. These
LEDs are driven from a spare pair of gates in IC6.
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Drive is sent from the micro controller circuit to each motor
driver board. The signals are in the form of five signals, four
signals drive the four FETs, and are independent of each other and
the motor drive enable signal.
As
mentioned
in
the
preliminary
text
describing
the
H
bridge
arrangement, drive is effective when one FET is held “on”, and
pulsed drive is made available to the other FET. This would be TR5
held on and TR8 pulsed with a variable pulse width to effect a
variable speed in one direction.
In the motor driver circuits, use of DC/DC voltage converters is
again put to good use. Originally a “Bootstrap” design was going
to be used, but by virtue of it’s design, you cannot achieve 100%
power through the controller to feed the drive motor. In this
design you can, because the drive bias is supplied from the DC/DC
converters and not the oscillating waveform from the motor drive
output. In a Bootstrap design, the drive has to be oscillating,
even at 99% drive, trying to achieve 100% drive would only turn
off the bias to the high FETs and the controller will switch off.
Failsafe Circuit Relay
Bearing in mind we have a supply of twenty four volts, it would
have been thought safe to assume the use of 24v relays would be
acceptable within this application. In use, the supply voltage
could actually drop below the minimum holding voltage which will
hold closed the relay contacts. When a 24v relay is actuated, it
could easily release a set the contacts when the supply voltage
drops to below 18v. Therefore the failsafe relay is a 12v device,
which has it's own 12v supply designed to power just this relay.
It should hold the relay voltage constant throughout these supply
transients. The overall power needed to supply the relay is a
little
higher,
but
this
is
the
price
we
have
to
pay
for
reliability in these circumstances.
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The failsafe relay is actuated and kept energised during normal
operation, but when the unit detects a failsafe condition, the
relay will become de-energised and removes power to the high power
circuits.
The
low
power
circuits
have
to
be
powered
during
failsafe. During the failsafe condition, the failsafe relay will
remain de-energised.
The
relay
driver
electronics
as
well
as
the
relay
coil
are
isolated from the micro controller circuit with an onboard optoisolator.
Motor Protection (over current) Circuit.
The FETs used in each motor driver are capable of handling a
maximum source current of 100 amps. This is internally limited by
the transistor’s own protection circuitry. TR6 and TR8 are both
known as “Intelligent Switches” and are a little more than just a
basic FET. They individually incorporate protection that limits
current
and
junction
temperature within
safe
operating
limits.
However to avoid this limit being reached during normal running,
except for starting surge, an additional circuit is incorporated
to detect and switch off the drive current. Once this limit has
been reached and sustained for a period of three seconds, the unit
will release the failsafe relay for a further five seconds, then
re-apply power.
This circuit can provide a non-intrusive means to sense the drive
motor currents, either through motors individually or the total
motor
drive
current
as
a
whole.
Therefore
one
or
two
sense
circuits can be employed. Or can be omitted.
The circuit uses a reed relay that during normal operation is kept
energised, the primary coil current is adjusted with the aid of
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Rv1 on the board. A secondary coil is wound around the outside of
the reed relay. The current in this secondary coil is made in such
a way that this additional magnetic field produced equals and
opposes the primary magnetic field generated from the five volt
supply when a fault condition occurs. During this fault condition
the secondary winding generates an opposing magnetic field to the
reed’s internal primary coil. The effect is that of opening the
reed switch contact when an equal and opposing magnetic field is
generated by the motor currents. Once opened for three seconds,
the
following
circuits
will
actuate
and
process
the
fault
information. The overload sense delay time is set by the time
constant of R2 and C1. However when the circuit is out of the
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K.R.Ginn
overload
state,
the
timing
components
of
R1
and
C1
are
now
effective, and the return out of the overload condition is almost
immediate.
The overload circuit integrates with the micro controller board,
where the signal is fed to pin 6 (RB0) on IC3, this port has a
Schmitt trigger input. During normal operation the reed relay RLA
contact is held closed whilst the primary coil is energised. Thus
being the motor drive currents fall below the overload threshold
current. It has to be mentioned the supplementary winding around
the
relay
has
to
have
the
motor
current
flow
in
the
right
direction to cancel the primary magnetic field generated by the
coil’s holding current. If the magnetic field generated by the
motor current is the wrong way around, the resultant additional
magnetic field will be augmented and the relay contact will never
open during a fault condition.
Motor Noise Suppression
Not shown in the circuit diagrams, for the sake of clarity are a
number of suppression components that have to be added to each
drive motor. Capacitors across the motor contacts, and from each
motor contact to the chassis of the motor are advised. This will
reduce the drive motor’s electrical noise significantly. Reducing
the effects on the R/C receiver. Additionally it has been found
prudent to also attach across the motor contacts a Varistor. The
Varistor acts as a transient voltage limiter, and keep any back
emfs
generated
by
the
motors
to
a
limit
of
50v.
The devices
themselves are rated at 47v and limit forward and reverse voltages
generated by the motors, i.e transients. This keeps any transients
generated by the drive motors well within the ratings of the motor
drive FETs.
Construction
File: IRC01.doc
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K.R.Ginn
The controller is fabricated from a total of six PCBs. They are as
follows:
1-
The micro controller and power supply circuit
2-
Left hand motor drive circuit
3-
Right hand drive circuit
4-
Failsafe relay driver
5-
Motor drive protection circuit (LHM)
6-
Motor drive protection circuit (RHM)
The micro controller and power supply circuits are fabricated on
one
double
sided PCB.
All the integrated
circuits, with the
exception of the three individual opto-isolators are mounted in IC
sockets.
The
turned
pin
variety
are
possibly
best
used
here,
thereby ensuring the IC won't shake loose in combat. The rest of
the components are all mounted snug to the boards, this way the
vibration to the components will not be too excessive. Observe
File: IRC01.doc
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K.R.Ginn
static
sensitive precautions
for
the appropriate
components in
this circuit and those on other boards in this project.
The
left
hand
and
right
hand
drive
motors
drive
boards
are
fabricated as a pair on two single-sided PCBs. All the components
are soldered in circuit. The 12v regulator and the power FETs for
each controller are mounted to a form of heat sinking, since they
will get hot during use. The regulator itself will dissipate about
one watt during operation. The mounting of the power devices has
to be checked, to ensure there are no electrical shorts or low
resistances caused from the actual device (drain terminal) to the
heat
sink
or
chassis
of
the
unit.
Use
thermal
grease
and
insulating washers to ensure good thermal coupling, if using mica
thermal washers. The majority of the wire links are made from a
small gauge tinned copper wire, approximately 24 swg will suffice.
However the use of a thicker gauge of wire is needed to help
supply current to the source of TR6, shown at the bottom right
hand of the PCB. The wire link between IC1 and R2 has to be
sleeved because of it’s proximity to the two smaller links either
side of it. A three way connector is avaialable on each motor
driver circuit as an auxillary 12 volts supply output from the 12
volt regulator. This could be used to drive a cooling fan allied
to the controller’s electronics. High current PCB tracks on this
board and others can be built up with the addition of solder run
along
the
track
making
the
tracks
thicker,
reducing
track
resistance.
Failsafe relay driver and the motor drive protection circuits are
constructed again on a single-sided PCB. IC1, the 12v regulator
requires heat sinking. This regulator will to get hot and will
dissipate about 1.5 watts when the failsafe relay is energised.
The FET used to switch the relay coil current is soldered onto the
underside of the PCB, and is a Surface Mount Device.
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K.R.Ginn
Most of the electronics circuits are accommodated in a die-cast
aluminium box for mechanical protection and heat sinking. Heat
sinking - especially for the two motor drive circuits; the casing
provides heat sinking for the main power components, these are
attached to the enclosure. The R/C receiver, weapons switcher and
the micro controller can all be accommodated within the same box.
There are a number of suppression components mounted close to the
drive motors, this can be accomplished as shown in one example
with all the components mounted in a small die-cast aluminium box
mounted on the actual drive motor.
The connection for the drive signals between the micro controller
board and the two motor driver circuits are made with the use of
two 10-way ribbon cables. These cables supply the drive signals to
the motor driver circuits from the micro-controller circuit. The
circuits either side of the cable are effectively isolated from
each
other
with
the
aid
of
the
opto-isolators
on
the
micro
controller board. The isolation provides a degree of immunity to
motor noise.
Mounting each PCB is accomplished with suitably sized spacers and
M3
screws
to
space
the
boards
away
from
the
casing.
In
the
prototype thin plastic sheeting (approximately 1mm thick) backs
each board to ensure there are no short circuits to the metal
case.
Wiring
The low current wiring in the unit, and this includes the power
feed to the micro-controller circuit board and the relay coils all
use
1
or
3
amp
cable.
The
remaining
high
power
circuits use
automotive wire cable of carrying the current needed to drive the
motors and ancillary circuits. Here the use of 30 amp wire has
been used, and purchased from a local automotive shop. In some
File: IRC01.doc
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K.R.Ginn
instances
the
circumstances)
wire
to
has
reduce
been
the
doubled
wire
(or
trebled
resistance
of
high
in
some
current
paths.
Main Power Link
The
main
power link that is required, is made of a “U” link
fabricated from a suitable connector which can handle the total
current with ease. The position of the link is made such that the
link can be accessed easily from the outside of the robot, and
removed without anyone or indeed anything coming to any harm. This
link will kill the electrical power totally to the robot and make
it safe.
Once
the
main
power
link
is
in
position
the
circuit
is
initialised, there is a half second delay which the failsafe relay
takes to power up the robot. This gives time for the electronics
to settle. At which point anyone close to the robot should get
clear, and retire to a safe distance before it starts working.
Testing and connecting up the units
It is probably best the five individual PCBs, once constructed are
tested on their own, without the need for a motor to be connected
to the driver circuits. As with any circuit, check the component
placements, ensuring
correct
orientation
of
the
components and
component values.
Power up each circuit in turn and check that no excessive current
is drawn from the power supply. For each circuit there should be
no greater current drawn than 30mA for any circuit at 24v supply
in their quiescent states. Set a current limit on the power supply
during testing to 500mA when testing individual boards, and start
the input voltage at 15 volts and rise it slowly to 24v. Do not
raise the voltage from zero to 24v, as this will inhibit any of
the DC/DC converters from starting up correctly. They otherwise
File: IRC01.doc
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K.R.Ginn
may draw a large current as a consequence. This will cause the
circuits not to work, and the DC/DC converters may get a little
warm. In testing this condition has not damaged any of the DC/DC
convertors.
Connect the circuits together on the bench with a current limited
power supply set to 2 amps at 24v. In place of the drive motor use
a
dummy
motor
circuit
that
can
be
made
from
a
handful
of
components. See figure 10.
This dummy motor circuit will lightly load the driver at 100mA,
and indicate which direction the current flows. Indicating to the
current
direction
flow
and
drive
level.
The
brighter
the
LED
glows, the greater amount of power is supplied to the motor and
hence the faster the motor will rotate. The other LED in the dummy
motor circuit will glow and indicate reverse current flow, this
indicates the speed of the motor running in reverse.
Connect the R/C receiver to the controller unit and switch on the
power
to
the circuit. Notice that
D4 on
the micro
controller
illuminates, so to does the LED on the two drive boards, D1. The
current drawn here should be in the order of 230mA. Don’t worry if
it is a little higher, but it should certainly be no greater than
500mA.
Check with the aid of a multi meter all the outputs from the
various regulators. This includes the input voltage to the micro
controller
board,
and
the
three
terminal
regulators
in
the
controller. Importantly, notice the high-end DC/DC converters on
the motor driver circuits are floating, and the output voltage
here is not with respect to earth or the negative side of the
supply.
Micro controller circuit.
File: IRC01.doc
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K.R.Ginn
Input
24v
with respect to earth (0v)
TR1 emitter
23v (approx).
IC1 DC/DC converter
12v.
IC2 input
11.4v.
IC2 output
5v
IC7, pin 16
12v supplied from the LHM driver board
IC8, pin 16
12v supplied from the RHM driver board
Motor driver boards (both).
IC5 input-
24v
IC1 output
12v
IC6
12v * note – floating, measure across the
DC/DC converters output.
Failsafe board
IC1 input
24v
IC1 output
12v
Overload protection circuit.
IC1 input
24v
IC1 output
12v
Set the preset potentiometer to 3 o’clock position.
Setting Up
When setting up, switch on the R/C transmitter before the robots
electronics.
Have
the
joystick
used
to
control
the
robot
centralized. Any adjustments should be made on the joystick’s trim
controls on the transmitter.
With
the
circuits
powered,
the
two
LEDs
on
micro
controller
circuit, D4 and D5 should remain unlit, so to will the LED on the
failsafe. The LEDs on the dummy motor boards may glow. Moving the
File: IRC01.doc
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K.R.Ginn
joystick back to the neutral position you will notice the LEDs on
the dummy motor boards light or extinguish. Moving the joystick
back the other LED on the dummy motor board will now illuminate.
The further away from the neutral position the joystick is the
brighter
the
LED
on
each
motor
driver
board
will
be.
Thus
indicating the motor running in the reverse direction.
With the drive levels we are dealing with during set up, there
should be no need to consider the protection circuitry, and the
setting up of this side as yet.
Add the actual drive motors in place of the dummy drive boards
with
the
suppression
circuitry
installed,
this
is
important.
Running tests with the motors on the bench is fairly safe, but
bear in mind the motors will tend run back and forward as the
testing progresses. You may find if the motors aren’t secured,
they may thrash around on the bench. Connecting the motors in
circuit and powering the whole controller from a series of gel
cell
batteries
currents.
will
Therefore
enable
during
large
bench
currents
testing
it
as
well
would
be
as
fault
wise
to
either limit the current with a suitably rated fuse or circuit
breaker.
As can been seen from the photos, there are a number of components
that
will
get
hot
or
warm
and
do
require
some
form
of
heat
sinking. Especially the power devices assigned to the motor driver
circuits. Specific details are not given, as the actual heat sink
dimensions
will
depend
largely
on
the
particular
installation
completed. The brackets fabricated are made from 16 swg aluminium
and are attached to the die-cast box in which the whole driver
circuits are installed. The casing thus forming part of the heat
sinking arrangement for the driver transistors.
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K.R.Ginn
After satisfactory testing on the bench, the controller can be
installed into the robot.
A word of warning.
When
checking
the
controller
in
the
robot
with
the
motors
connected, ensure the wheels are well clear of the floor or any
other object. Any weapon or similar device is secured in a safe
condition. Leave a good few inches clearance between the wheels
and the ground. Also between the wheels, any tools or loose pieces
of metal etc.
Switch
on
energise,
the
R/C
transmitter,
the
current
drawn
the
by
failsafe
the
relay
circuit
should
will
now
increase
accordingly when the relay is energised. Ensure the pulse width
received is between approximately 1.0 and 2.0mS, otherwise the
unit will fall into failsafe.
Set
the
corresponding
joystick
controls
on
the
transmitter
to
their central position. Here we have to assume the joystick’s
central position corresponds to a pulse width at the receiver
servo output of 1.5mS. Using an oscilloscope here will be very
useful in verifying this pulse width. With both joysticks, one
assigned for steering, the other assigned to speed control set in
their central positions the motors (or dummy load motors) should
show no signs of life. The failsafe relay will be energised, and
the shown by the LED illuminated on the failsafe PCB.
Pushing now the steering joystick to the left will see the LED D4
illuminate on the micro controller board, pushing the joystick to
the
right,
D5
will
extinguish
and
D4
will
illuminate.
This
indicates the PIC assigned for steering is working and decoding
the receiver pulse width correctly for the turn information. Relocating the joystick to the central position, LEDs, D4 and D5
should both extinguish.
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K.R.Ginn
Looking at the joystick assigned to control the speed of the drive
motors and moving the joystick forward, a forward drive condition
will be initialised, and the LED on the dummy motor load board for
both motors will illuminate/flash, and will get brighter as more
the joystick is progressively pushed forward.
Connecting the drive motors to the circuit it is prudent to switch
the controller off and let it lay un-powered for a at least ten
seconds before attempting to attach the motors. Once the motors
have been connected keep the drive wheels chocked up and off the
ground.
Apply
the
high current link,
still
with the
fuse
(or circuit
breaker) in circuit. Stand clear!
With the transmitter switched on and the controller powered the
robot’s wheels should be stationary. Moving the joystick gently
forward both motors will begin to slowly rotate, hopefully to
propel the robot forward. Slowly returning the joystick to the
central position the motor will slow and stop. Pull the joystick
toward
you
and
both
the
wheels
will
rotate
in
the
opposite
direction. Return the joystick to the neutral position.
Actuate
the
steering
joystick
to
the
left,
push
the
joystick
controlling speed forward. You will now notice the right hand
motor driving forward, whilst the left hand motor is driving in
reverse, effecting a forward left hand turn. Return both joysticks
slowly to their neutral positions. Move the steering joystick to
the right, and the speed joystick to the forward position, notice
now the rotation of the drive motors is opposite to what it was
before, initiating a forward right hand turn.
Failsafe operation.
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K.R.Ginn
The operation of the failsafe circuit has to be checked before the
robot is unleashed on another unsuspected robot. Once the joystick
trims have been adjusted on the R/C transmitter; setting up the
neutral position for both speed and steering, and the extremes of
joystick travel which must be within the acceptable limits, i.e.
0.9 to 2.1mS. If the receiver pulse width were to enter outside
this window, the controller would fall immediately into a failsafe
condition.
The
failsafe
on
the
prototype
was
found
to
be
successful in operation, and the software filtering is adiquate.
In testing the prototype robot’s wheels were not perceived to have
moved more than a few degrees, in an hours soak test.
Checking the Robot’s Failsafe
Checking the robot’s failsafe is done in the following manner.
Ensure the safety link is removed from the robot and it is unpowered. Check to the transmitter is switched off. Always switch
the robot on last of the two parts, this being the transmitter is
always switched on first before the robot, and is always switched
off last when the robot is switched off.
With the transmitter powered, connect the main power link to the
robot, power will be initialised to the circuitry, and the robot
will become active to commands after a delay of two seconds. Use
the joysticks to verify the operation of the radio link. Switch
off
the
transmitter,
and
the
failsafe
relay
will
become
de-
energised. The motors will run down and should remain in-active
whilst the failsafe condition prevails. Any weapon under control
of
the
failsafe
should
will
also
remain
in-active
during
the
failsafe condition. Should electrical noise trigger any part of
the circuit, it should only be momentary, and movement of the
robot will be minimal. The failsafe has been active for an hours
test and in that time no discernable movement of the robot was
observed, nor did the weapon trigger once.
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K.R.Ginn
The reason for slowly moving the joysticks back and forth is to
ensure
the
starting
current
is
not
sufficient
to
trip
the
temporary fuse or circuit breaker in the main power line used to
protect the circuits during testing. This can be removed once the
testing
has
been
completed
and
are
confident
the
controller
circuit is sound.
Once the power line protection has been removed after testing, the
robot can be checked out in a safe area. Testing the robot with
the R/C equipment fully operational. Good luck!
Component List (micro controller board)
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24
R25
R26
R28
R29
R30
R31
R32
C1
220R 600mW
1K0
4K7
22K
22K
1K2
1K0
470R
470R
470R
470R
470R
470R
470R
470R
470R
4K3
4K3
4K3
4K3
4K3
220R
4K3
4K3
4K3
4K3
4K7
1K8
1K8
22K
2K2
470uF 35v PCB mounting elect, 0.2”
File: IRC01.doc
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K.R.Ginn
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
D1
D2
D3
D4
D5
D6
TR1
IC1
10uF 35v PCB mounting elect, 0.1”
4700uF 16v PCB mounting elect, 0.3”
4700uF 16v PCB mounting elect, 0.3”
4700uF 16v PCB mounting elect, 0.3”
100nF 63v poly PCB mounting 0.2”
47uF 50v PCB mounting elect, 0.1”
100nF 63v poly PCB mounting 0.2”
22pF ceramic PCB mounting 0.1”
22pF ceramic PCB mounting 0.1”
100nF 63v poly PCB mounting 0.2”
220uF 35v PCB mounting elect 0.2”
100nF 63v poly PCB mounting 0.2”
100nF 63v poly PCB mounting 0.2”
47uF 50v PCB mounting elect, 0.1”
100nF 63v poly PCB mounting 0.2”
1N4002
27v 1.3w zener diode
1N4002
3mm red LED, 0.1”
3mm green LED 0.1”
3mm yellow LED 0.1”
TIP41C, plus insulating kit.
24v/12v 3 3watt DC/DC converter, manufacturers part no:
NDY2412, Farnell stock no: 605-633
IC2
LM2940CT, 5v three terminal regulator, plus insulating
washer.
IC3 PIC16F84-4
IC4 PIC16F84-4
IC5 74LS09
IC6 74LS86
IC7 TL074 quad opto-isolator, Maplin stock no: YY63T
IC8 SHF618-2 single opto-isolator, Maplin stock no: CY94C
IC9 TL074 quad opto-isolator, Maplin stock no: YY63T
IC10 SHF618-2 single opto-isolator, Maplin stock no: CY94C
IC11 SHF618-2 single opto-isolator, Maplin stock no: CY94C
Misc Components
Connectors, Varistor 39v, Farnell stock no: 318-401. PCB mounting,
3-way, 4-way, 5 way and 10way, **see circuit diagram. DIL sockets14,16 and 18 pins. Mounting hardware, screws etc.
Component List (motor
components below)
R1
R2
R3
R4
driver
board,
2
required
of
listed
2K2
10K
1K8
22R
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K.R.Ginn
R5
R6
R7
R8
R9
R10
R11
R12
R13
R14
R15
R16
R17
R18
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
D1
ZD1
ZD2
ZD3
ZD4
IC1
IC2
IC3
IC4
IC5
IC6
IC7
TR1
TR2
TR3
TR4
TR5
TR6
TR7
TR8
100K
1K8
22R
2K2
10K
1K8
22R
4K7
100K
2K2
1K8
22R
2K2
2K2
10uF 50v PCB mounting elect, 0.1”
100uF 25v PCB mounting elect, 0.1”
100nF 63v poly PCB mounting 0.2”
100nF 63v poly PCB mounting 0.2”
100nF 63v poly PCB mounting 0.2”
100nF 63v poly PCB mounting 0.2”
100uF 25v PCB mounting elect, 0.1”
10nF 63v poly PCB mounting 0.2”
100uF 25v PCB mounting elect, 0.1”
10nF 63v poly PCB mounting 0.2”
red LED, 0.1”
15v 300mW zener diode
15v 300mW zener diode
15v 300mW zener diode
15v 300mW zener diode
SHF618-2 single opto-isolator, Maplin stock no: CY94C
SHF618-2 single opto-isolator, Maplin stock no: CY94C
HEF4011BP
HEF4011BP
12v 1 amp 3-terminal regulator – 7812, with heat sink
12v/12v 1 watt DC/DC converter, manufacturers part no:
NME1212S, Farnell part no: 178-197
12v/12v 1 watt DC/DC converter, manufacturers part no:
NME1212S, Farnell part no: 178-197
BC182L
BC182L
BC182L
BC182L
FQA85N06, Farnell stock no: 394-4384
VNW100N04, Farnell stock no: 332-8569
FQA85N06, Farnell stock no: 394-4384
VNW100N04, Farnell stock no: 332-8569
Misc Components
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K.R.Ginn
Connectors
Insulating
10
way,
washers
and
for
IC5,
connecting
TR5
to
and
TR8,
mounting
and
heat
hardware.
sink
to
be
fabricated.
Component List (Failsafe relay board)
R1
R2
R3
C1
C2
C3
D1
TR1
IC1
100K
1KO
2K2
100nF 63v poly PCB mounting 0.2”
100nF 63v poly PCB mounting 0.2”
22uF 35v PCB mounting elect, 0.1”
RED led, 0.1”
BSP295, SMD FET
7812 12v 1 amp 3-terminal regulator and heat sink
Misc Components
Connectors, 30 amp DPST 12v relay, PCB mounting 2-5 way and one 4way, see circuit diagram.
Component List (Overload board)
R1
470R
R2
56K
R3
1K0
R4
1K0
Rv1 100R preset
C1
100uF 25v PCB mounting elect 0.1” pitch
C2
47uF 25v radial mounting elect
D1
5v6 600mW zener diode
D2
1N4148
D3
3mm red LED, 0.1” pitch
TR1 2N3703
TR2 BC182L
RLA reed relay SPNO 5v, coil resistance 500R. Maplin stock no:
JH12N
Misc Components
Connectors, PCB 5 way plugs, 14swg (2.00mm diameter)tinned copper
wire, PCB
Component List (Motor suppression, one set per motor)
100nF 200v polyester capacitors (3 required).
Varistor 39v, Farnell stock no: 318-401.
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K.R.Ginn
Component availability.
The
components
suppliers,
the
for
most
this
project
common
were
sourced
components,
i.e.
from
two
resistors
main
and
capacitors are obtainable from common suppliers, in this instance
Maplin. The more specialised components such as the power FETs and
the
DC/DC
converters
were
sourced
from
one
specific
supplier,
Farnell. The PCBs can be obtained from the EPE PCB service.
Additional notes from construction not necessarily for publication
– KG).
The prototype PCBs were sourced from two suppliers after design.
They were PCB-Pool in Ireland for the double-sided board. The
single sided PCBs were sourced from a company in Erith, P & D
Circuits through a friend of mine who manufacturers short runs for
me.
The whole unit was fabricated as presented. The majority of the
circuitry was enclosed within the die-cast box and mounted to the
rear wall of the robot. The die-cast box forming part of the heat
sinking for the power FETs and protection against flying metal
objects and shards of metal within the robot. The exception is the
overload circuits both of which are temporarily mounted on the
outside of the unit with Velcro. A more permanent solution will be
made in time, i.e. brackets.
The controller was primarily designed for the two wheel chair
motors, and does work very well with these two 150 watt motors. I
see no reason why the controller can’t be used with higher power
motors running at 24 volts. Only the overload circuit and high
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K.R.Ginn
current cabling should be changed accordingly to cope with the
higher current.
On the micro-controller PCB R32 is not shown in the prototype,
this actual resistor has been added to the bottom of the PCB. But
in the published version, this has been added to the finished
board and is adjacent to IC3, right hand side.
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K.R.Ginn